[PATCH 1/2] Ext4Pkg: Improve extent node validation on the number of entries

[PATCH 1/2] Ext4Pkg: Improve extent node validation on the number of entries

[Pedro Falcato]

Improve the extent tree node validation by validating the number of
entries the node advertises against the theoretical max (derived from
the size of on-disk structs and the block size (or i_data, if inline
extents).

Previously, we did not validate the number of entries. This could be
exploited for out-of-bounds reads and crashes.

Cc: Marvin Häuser <mhaeuser@posteo.de>
Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
Reported-by: Savva Mitrofanov <savvamtr@gmail.com>
Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
---
 Features/Ext4Pkg/Ext4Dxe/Extents.c | 47 +++++++++++++++++++-----------
 1 file changed, 30 insertions(+), 17 deletions(-)

diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c b/Features/Ext4Pkg/Ext4Dxe/Extents.c
index 9e4364e50d99..66d085938549 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Extents.c
+++ b/Features/Ext4Pkg/Ext4Dxe/Extents.c
@@ -1,7 +1,7 @@
 /** @file
   Extent related routines
 
-  Copyright (c) 2021 - 2022 Pedro Falcato All rights reserved.
+  Copyright (c) 2021 - 2023 Pedro Falcato All rights reserved.
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
@@ -80,13 +80,15 @@ Ext4GetInoExtentHeader (
 /**
    Checks if an extent header is valid.
    @param[in]      Header         Pointer to the EXT4_EXTENT_HEADER structure.
+   @param[in]      MaxEntries     Maximum number of entries possible for this tree node.
 
    @return TRUE if valid, FALSE if not.
 **/
 STATIC
 BOOLEAN
 Ext4ExtentHeaderValid (
-  IN CONST EXT4_EXTENT_HEADER  *Header
+  IN CONST EXT4_EXTENT_HEADER  *Header,
+  IN UINT16                    MaxEntries
   )
 {
   if (Header->eh_depth > EXT4_EXTENT_TREE_MAX_DEPTH) {
@@ -99,6 +101,18 @@ Ext4ExtentHeaderValid (
     return FALSE;
   }
 
+  if ((Header->eh_max > MaxEntries) || (Header->eh_entries > MaxEntries)) {
+    DEBUG ((
+      DEBUG_ERROR,
+      "[ext4] Invalid extent header entries (extent header: %u max,"
+      " %u entries, theoretical max: %u) (larger than permitted)\n",
+      Header->eh_max,
+      Header->eh_entries,
+      MaxEntries
+      ));
+    return FALSE;
+  }
+
   if (Header->eh_max < Header->eh_entries) {
     DEBUG ((
       DEBUG_ERROR,
@@ -212,6 +226,9 @@ Ext4ExtentIdxLeafBlock (
   return LShiftU64 (Index->ei_leaf_hi, 32) | Index->ei_leaf_lo;
 }
 
+// Results of sizeof(i_data) / sizeof(extent) - 1 = 4
+#define EXT4_NR_INLINE_EXTENTS  4
+
 /**
    Retrieves an extent from an EXT4 inode.
    @param[in]      Partition     Pointer to the opened EXT4 partition.
@@ -237,7 +254,7 @@ Ext4GetExtent (
   EXT4_EXTENT_HEADER  *ExtHeader;
   EXT4_EXTENT_INDEX   *Index;
   EFI_STATUS          Status;
-  EXT4_BLOCK_NR       BlockNumber;
+  UINT32              MaxExtentsPerNode;
 
   Inode  = File->Inode;
   Ext    = NULL;
@@ -275,12 +292,17 @@ Ext4GetExtent (
 
   ExtHeader = Ext4GetInoExtentHeader (Inode);
 
-  if (!Ext4ExtentHeaderValid (ExtHeader)) {
+  if (!Ext4ExtentHeaderValid (ExtHeader, EXT4_NR_INLINE_EXTENTS)) {
     return EFI_VOLUME_CORRUPTED;
   }
 
   CurrentDepth = ExtHeader->eh_depth;
 
+  // A single node fits into a single block, so we can only have (BlockSize / sizeof(EXT4_EXTENT)) - 1
+  // extents in a single node. Note the -1, because both leaf and internal node headers are 12 bytes,
+  // and so are individual entries.
+  MaxExtentsPerNode = (Partition->BlockSize / sizeof (EXT4_EXTENT)) - 1;
+
   while (ExtHeader->eh_depth != 0) {
     CurrentDepth--;
     // While depth != 0, we're traversing the tree itself and not any leaves
@@ -289,17 +311,7 @@ Ext4GetExtent (
     // Therefore, we can use binary search, and it's actually the standard for doing so
     // (see FreeBSD).
 
-    Index       = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
-    BlockNumber = Ext4ExtentIdxLeafBlock (Index);
-
-    // Check that block isn't file hole
-    if (BlockNumber == EXT4_BLOCK_FILE_HOLE) {
-      if (Buffer != NULL) {
-        FreePool (Buffer);
-      }
-
-      return EFI_VOLUME_CORRUPTED;
-    }
+    Index = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
 
     if (Buffer == NULL) {
       Buffer = AllocatePool (Partition->BlockSize);
@@ -309,7 +321,8 @@ Ext4GetExtent (
     }
 
     // Read the leaf block onto the previously-allocated buffer.
-    Status = Ext4ReadBlocks (Partition, Buffer, 1, BlockNumber);
+
+    Status = Ext4ReadBlocks (Partition, Buffer, 1, Ext4ExtentIdxLeafBlock (Index));
     if (EFI_ERROR (Status)) {
       FreePool (Buffer);
       return Status;
@@ -317,7 +330,7 @@ Ext4GetExtent (
 
     ExtHeader = Buffer;
 
-    if (!Ext4ExtentHeaderValid (ExtHeader)) {
+    if (!Ext4ExtentHeaderValid (ExtHeader, MaxExtentsPerNode)) {
       FreePool (Buffer);
       return EFI_VOLUME_CORRUPTED;
     }
-- 
2.40.1

[PATCH 2/2] Ext4Pkg: Advertise CSUM_SEED as supported

[Pedro Falcato]

We had added support for CSUM_SEED but accidentally forgot to advertise
it in gSupportedIncompatFeat. This made it (erroneously) impossible to
mount CSUM_SEED filesystems.

Detected by attempting to mount a relatively new mkfs.ext4'd filesystem.

Cc: Marvin Häuser <mhaeuser@posteo.de>
Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
---
 Features/Ext4Pkg/Ext4Dxe/Superblock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Features/Ext4Pkg/Ext4Dxe/Superblock.c b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
index 3f56de93c105..604925b582c1 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Superblock.c
+++ b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
@@ -1,7 +1,7 @@
 /** @file
   Superblock managing routines
 
-  Copyright (c) 2021 - 2022 Pedro Falcato All rights reserved.
+  Copyright (c) 2021 - 2023 Pedro Falcato All rights reserved.
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
@@ -18,7 +18,7 @@ STATIC CONST UINT32  gSupportedIncompatFeat =
   EXT4_FEATURE_INCOMPAT_64BIT | EXT4_FEATURE_INCOMPAT_DIRDATA |
   EXT4_FEATURE_INCOMPAT_FLEX_BG | EXT4_FEATURE_INCOMPAT_FILETYPE |
   EXT4_FEATURE_INCOMPAT_EXTENTS | EXT4_FEATURE_INCOMPAT_LARGEDIR |
-  EXT4_FEATURE_INCOMPAT_MMP | EXT4_FEATURE_INCOMPAT_RECOVER;
+  EXT4_FEATURE_INCOMPAT_MMP | EXT4_FEATURE_INCOMPAT_RECOVER | EXT4_FEATURE_INCOMPAT_CSUM_SEED;
 
 // Future features that may be nice additions in the future:
 // 1) Btree support: Required for write support and would speed up lookups in large directories.
-- 
2.40.1

Re: [PATCH 1/2] Ext4Pkg: Improve extent node validation on the number of entries

[Marvin Häuser]

> On 9. May 2023, at 02:42, Pedro Falcato <pedro.falcato@gmail.com> wrote:
> 
> Improve the extent tree node validation by validating the number of
> entries the node advertises against the theoretical max (derived from
> the size of on-disk structs and the block size (or i_data, if inline
> extents).
> 
> Previously, we did not validate the number of entries. This could be
> exploited for out-of-bounds reads and crashes.
> 
> Cc: Marvin Häuser <mhaeuser@posteo.de>
> Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
> Reported-by: Savva Mitrofanov <savvamtr@gmail.com>
> Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
> ---
> Features/Ext4Pkg/Ext4Dxe/Extents.c | 47 +++++++++++++++++++-----------
> 1 file changed, 30 insertions(+), 17 deletions(-)
> 
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c b/Features/Ext4Pkg/Ext4Dxe/Extents.c
> index 9e4364e50d99..66d085938549 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Extents.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/Extents.c
> @@ -1,7 +1,7 @@
> /** @file
>   Extent related routines
> 
> -  Copyright (c) 2021 - 2022 Pedro Falcato All rights reserved.
> +  Copyright (c) 2021 - 2023 Pedro Falcato All rights reserved.
>   SPDX-License-Identifier: BSD-2-Clause-Patent
> **/
> 
> @@ -80,13 +80,15 @@ Ext4GetInoExtentHeader (
> /**
>    Checks if an extent header is valid.
>    @param[in]      Header         Pointer to the EXT4_EXTENT_HEADER structure.
> +   @param[in]      MaxEntries     Maximum number of entries possible for this tree node.
> 
>    @return TRUE if valid, FALSE if not.
> **/
> STATIC
> BOOLEAN
> Ext4ExtentHeaderValid (
> -  IN CONST EXT4_EXTENT_HEADER  *Header
> +  IN CONST EXT4_EXTENT_HEADER  *Header,
> +  IN UINT16                    MaxEntries
>   )
> {
>   if (Header->eh_depth > EXT4_EXTENT_TREE_MAX_DEPTH) {
> @@ -99,6 +101,18 @@ Ext4ExtentHeaderValid (
>     return FALSE;
>   }
> 
> +  if ((Header->eh_max > MaxEntries) || (Header->eh_entries > MaxEntries)) {

For eh_entries, this is implicit via the check below.

> +    DEBUG ((
> +      DEBUG_ERROR,
> +      "[ext4] Invalid extent header entries (extent header: %u max,"
> +      " %u entries, theoretical max: %u) (larger than permitted)\n",
> +      Header->eh_max,
> +      Header->eh_entries,
> +      MaxEntries
> +      ));
> +    return FALSE;
> +  }
> +
>   if (Header->eh_max < Header->eh_entries) {
>     DEBUG ((
>       DEBUG_ERROR,
> @@ -212,6 +226,9 @@ Ext4ExtentIdxLeafBlock (
>   return LShiftU64 (Index->ei_leaf_hi, 32) | Index->ei_leaf_lo;
> }
> 
> +// Results of sizeof(i_data) / sizeof(extent) - 1 = 4
> +#define EXT4_NR_INLINE_EXTENTS  4
> +
> /**
>    Retrieves an extent from an EXT4 inode.
>    @param[in]      Partition     Pointer to the opened EXT4 partition.
> @@ -237,7 +254,7 @@ Ext4GetExtent (
>   EXT4_EXTENT_HEADER  *ExtHeader;
>   EXT4_EXTENT_INDEX   *Index;
>   EFI_STATUS          Status;
> -  EXT4_BLOCK_NR       BlockNumber;
> +  UINT32              MaxExtentsPerNode;
> 
>   Inode  = File->Inode;
>   Ext    = NULL;
> @@ -275,12 +292,17 @@ Ext4GetExtent (
> 
>   ExtHeader = Ext4GetInoExtentHeader (Inode);
> 
> -  if (!Ext4ExtentHeaderValid (ExtHeader)) {
> +  if (!Ext4ExtentHeaderValid (ExtHeader, EXT4_NR_INLINE_EXTENTS)) {
>     return EFI_VOLUME_CORRUPTED;
>   }
> 
>   CurrentDepth = ExtHeader->eh_depth;
> 
> +  // A single node fits into a single block, so we can only have (BlockSize / sizeof(EXT4_EXTENT)) - 1
> +  // extents in a single node. Note the -1, because both leaf and internal node headers are 12 bytes,
> +  // and so are individual entries.
> +  MaxExtentsPerNode = (Partition->BlockSize / sizeof (EXT4_EXTENT)) - 1;
> +
>   while (ExtHeader->eh_depth != 0) {
>     CurrentDepth--;
>     // While depth != 0, we're traversing the tree itself and not any leaves
> @@ -289,17 +311,7 @@ Ext4GetExtent (
>     // Therefore, we can use binary search, and it's actually the standard for doing so
>     // (see FreeBSD).
> 
> -    Index       = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
> -    BlockNumber = Ext4ExtentIdxLeafBlock (Index);
> -
> -    // Check that block isn't file hole
> -    if (BlockNumber == EXT4_BLOCK_FILE_HOLE)

Why is this no longer possible?

Best regards,
Marvin

> {
> -      if (Buffer != NULL) {
> -        FreePool (Buffer);
> -      }
> -
> -      return EFI_VOLUME_CORRUPTED;
> -    }
> +    Index = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
> 
>     if (Buffer == NULL) {
>       Buffer = AllocatePool (Partition->BlockSize);
> @@ -309,7 +321,8 @@ Ext4GetExtent (
>     }
> 
>     // Read the leaf block onto the previously-allocated buffer.
> -    Status = Ext4ReadBlocks (Partition, Buffer, 1, BlockNumber);
> +
> +    Status = Ext4ReadBlocks (Partition, Buffer, 1, Ext4ExtentIdxLeafBlock (Index));
>     if (EFI_ERROR (Status)) {
>       FreePool (Buffer);
>       return Status;
> @@ -317,7 +330,7 @@ Ext4GetExtent (
> 
>     ExtHeader = Buffer;
> 
> -    if (!Ext4ExtentHeaderValid (ExtHeader)) {
> +    if (!Ext4ExtentHeaderValid (ExtHeader, MaxExtentsPerNode)) {
>       FreePool (Buffer);
>       return EFI_VOLUME_CORRUPTED;
>     }
> -- 
> 2.40.1
> 

Re: [PATCH 2/2] Ext4Pkg: Advertise CSUM_SEED as supported

[Marvin Häuser]

Reviewed-by: Marvin Häuser <mhaeuser@posteo.de>

> On 9. May 2023, at 02:42, Pedro Falcato <pedro.falcato@gmail.com> wrote:
> 
> We had added support for CSUM_SEED but accidentally forgot to advertise
> it in gSupportedIncompatFeat. This made it (erroneously) impossible to
> mount CSUM_SEED filesystems.
> 
> Detected by attempting to mount a relatively new mkfs.ext4'd filesystem.
> 
> Cc: Marvin Häuser <mhaeuser@posteo.de>
> Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
> ---
> Features/Ext4Pkg/Ext4Dxe/Superblock.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Superblock.c b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
> index 3f56de93c105..604925b582c1 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Superblock.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
> @@ -1,7 +1,7 @@
> /** @file
>   Superblock managing routines
> 
> -  Copyright (c) 2021 - 2022 Pedro Falcato All rights reserved.
> +  Copyright (c) 2021 - 2023 Pedro Falcato All rights reserved.
>   SPDX-License-Identifier: BSD-2-Clause-Patent
> **/
> 
> @@ -18,7 +18,7 @@ STATIC CONST UINT32  gSupportedIncompatFeat =
>   EXT4_FEATURE_INCOMPAT_64BIT | EXT4_FEATURE_INCOMPAT_DIRDATA |
>   EXT4_FEATURE_INCOMPAT_FLEX_BG | EXT4_FEATURE_INCOMPAT_FILETYPE |
>   EXT4_FEATURE_INCOMPAT_EXTENTS | EXT4_FEATURE_INCOMPAT_LARGEDIR |
> -  EXT4_FEATURE_INCOMPAT_MMP | EXT4_FEATURE_INCOMPAT_RECOVER;
> +  EXT4_FEATURE_INCOMPAT_MMP | EXT4_FEATURE_INCOMPAT_RECOVER | EXT4_FEATURE_INCOMPAT_CSUM_SEED;
> 
> // Future features that may be nice additions in the future:
> // 1) Btree support: Required for write support and would speed up lookups in large directories.
> -- 
> 2.40.1
>